Light emitting diode

ABSTRACT

A light emitting diode includes a carbon nanotube layer, a first semiconductor layer, a second semiconductor layer, an active layer, a first electrode and a second electrode stacked on an epitaxial growth surface of a substrate. A first part of the carbon nanotube layer is covered by the first semiconductor layer and a second part of the carbon nanotube layer is exposed. The first electrode is electrically connected with the second semiconductor layer and the second electrode electrically is connected with the second part of the carbon nanotube layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application 201110110751.5, filed on Apr. 29, 2011 in theChina Intellectual Property Office, the disclosure of which isincorporated herein by reference. This application is related toapplications entitled, “METHOD FOR MAKING LIGHT EMITTING DIODE”, filed______ (Atty. Docket No. US39404); “LIGHT EMITTING DIODE”, filed ______(Atty. Docket No. US39405); “METHOD FOR MAKING LIGHT EMITTING DIODE”,filed ______ (Atty. Docket No. US39406); “LIGHT EMITTING DIODE”, filed______ (Atty. Docket No. US39408); “METHOD FOR MAKING LIGHT EMITTINGDIODE”, filed ______ (Atty. Docket No. US39409); “LIGHT EMITTING DIODE”,filed ______ (Atty. Docket No. US39411); “METHOD FOR MAKING LIGHTEMITTING DIODE”, filed ______ (Atty. Docket No. US39412); “LIGHTEMITTING DIODE”, filed ______ (Atty. Docket No. US39413); “METHOD FORMAKING LIGHT EMITTING DIODE”, filed ______ (Atty. Docket No. US39414);“LIGHT EMITTING DIODE”, filed ______ (Atty. Docket No. US39415); “METHODFOR MAKING LIGHT EMITTING DIODE”, filed ______ (Atty. Docket No.US39416). The disclosures of the above-identified applications areincorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a light emitting diode (LED) and amethod for making the same.

2. Description of the Related Art

LEDs are semiconductors that convert electrical energy into light.Compared to conventional light sources, the LEDs have higher energyconversion efficiency, higher radiance (i.e., they emit a largerquantity of light per unit area), longer lifetime, higher responsespeed, and better reliability. At the same time, LEDs generate lessheat. Therefore, LED modules are widely used as light sources in opticalimaging systems, such as displays, projectors, and so on.

A conventional LED commonly includes an N-type semiconductor layer, aP-type semiconductor layer, an active layer, an N-type electrode, and aP-type electrode. The active layer is located between the N-typesemiconductor layer and the P-type semiconductor layer. The P-typeelectrode is located on the P-type semiconductor layer. The N-typeelectrode is located on the N-type semiconductor layer. Typically, theP-type electrode is transparent. In operation, a positive voltage and anegative voltage are applied respectively to the P-type semiconductorlayer and the N-type semiconductor layer. Thus, holes in the P-typesemiconductor layer and electrons in the N-type semiconductor layer canenter the active layer and combine with each other to emit visiblelight.

However, extraction efficiency of LEDs is low because typicalsemiconductor materials have a higher refraction index than that of air.Large-angle light emitted from the active layer may be internallyreflected in LEDs, so that a large portion of the light emitted from theactive layer will remain in the LEDs, thereby degrading the extractionefficiency.

What is needed, therefore, is a light emitting diode and a method formaking the same, which can overcome the above-described shortcomings

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referenceto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a flowchart of one embodiment a method for manufacturing aLED.

FIG. 2 shows a Scanning Electron Microscope (SEM) image of oneembodiment of a drawn carbon nanotube film.

FIG. 3 shows a schematic view of one embodiment of a carbon nanotubesegment of a drawn carbon nanotube film.

FIG. 4 shows a SEM image of one embodiment of a plurality of carbonnanotube films which are stacked in a crossed manner.

FIG. 5 shows a SEM image of one embodiment of an untwisted carbonnanotube wire.

FIG. 6 shows a SEM image of one embodiment of a twisted carbon nanotubewire.

FIG. 7 shows a schematic view of growing an epitaxial layer.

FIG. 8 shows a three-dimensional view of one embodiment of a LEDfabricated according to the method of FIG. 1.

FIG. 9 is a schematic, cross-sectional view, along a line IX-IX of FIG.8.

FIG. 10 shows a SEM of a cross-section of the junction between thesemiconductor epitaxial layer and the substrate.

FIG. 11 show a Transmission Electron Microscopy (TEM) image of magnifiedpart of FIG. 10

FIG. 12 is a cross-section view of one embodiment of a LED.

FIG. 13 is a cross-section view of another embodiment of a LED.

FIG. 14 is a three-dimensional view of one embodiment of a LED.

FIG. 15 is a three-dimensional view of another embodiment of a LED.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIG. 1, a method for manufacturing a light emitting diode(LED) 10 includes the following steps:

(S10) providing a substrate 100 having an epitaxial growth surface 101;

(S20) applying a carbon nanotube layer 102 on the epitaxial growthsurface 101;

(S30) growing a semiconductor epitaxial layer 104 on the epitaxialgrowth surface 101, wherein the semiconductor epitaxial layer 104includes an N-type semiconductor layer 106, an active layer 107 and aP-type semiconductor layer 108;

(S40) exposing a part of the carbon nanotube layer 102 by etching thesemiconductor epitaxial layer 104; and

(S50) applying a first electrode 110 on the semi-conductor layer 104 anda second electrode 112 on the carbon nanotube layer 102, wherein thefirst electrode 110 is deposited on a surface of the semiconductor layer104, and the second electrode 112 is deposited on the exposed part ofthe carbon nanotube layer 102 at the epitaxial growth surface 101.

In step (S10), the epitaxial growth surface 101 is used to grow thesemiconductor epitaxial layer 104. The epitaxial growth surface 101 is avery smooth surface. Oxygen and carbon are removed from the surface. Thesubstrate 100 can be a single layer structure or a multiple layerstructure. If the substrate 100 is a single layer structure, thesubstrate 100 can be a single-crystal structure. The single-crystalstructure includes a crystal face which is used as the epitaxial growthsurface 101. The material of the substrate 100 can be SOI (Silicon oninsulator), LiGaO₂, LiAlO₂, Al₂O₃, Si, GaAs, GaN, GaSb, InN, InP, InAs,InSb, AlP, AlAs, AlSb, AlN, GaP, SiC, SiGe, GaMnAs, GaAlAs, GaInAs,GaAlN, GaInN, AlInN, GaAsP, InGaN, AlGaInN, AlGaInP, GaP:Zn or GaP:N.The material of the substrate 100 is not limited, as long as thesubstrate 100 has an epitaxial growth surface 101 on which N-typesemiconductor layer 106 can grow. If the substrate 100 is a multiplelayer structure, the substrate 100 should include at least one layer ofthe single-crystal structure mentioned previously. The material of thesubstrate 100 can be selected according to N-type semiconductor layer106. In one embodiment, the lattice constant and thermal expansioncoefficient of the substrate 100 is similar to N-type semiconductorlayer 106 thereof in order to improve the quality of N-typesemiconductor layer 106. In another embodiment, the material of thesubstrate 100 is sapphire. The thickness, shape, and size of thesubstrate 100 are arbitrary and can be selected according to need.

In step (S20), the thickness of the carbon nanotube layer 102 rangesfrom about 1 nanometer to about 100 micrometers, such as 10 nanometers,200 nanometers, or 1 micrometer. The carbon nanotube layer 102 is apatterned structure. In one embodiment, the carbon nanotube layer 102 isabout 100 nanometers in thickness. The carbon nanotubes of the carbonnanotube layer 102 can be single-walled carbon nanotubes, double-walledcarbon nanotubes, or multi-walled carbon nanotubes. The length anddiameter of the carbon nanotubes can be selected according to need.Because the carbon nanotube layer 102 is a patterned structure, when thecarbon nanotube layer 102 is applied on the epitaxial surface 101, someportions of the epitaxial surface 101 will be exposed to grow N-typesemiconductor layer 106. Thus the carbon nanotube layer 102 is used as amask layer.

The term “patterned structure” means that the carbon nanotube layer 102defines a plurality of apertures 105 penetrating the carbon nanotubelayer 102 perpendicular to the surface of the carbon nanotube layer 102.The apertures 105 can be micro-holes formed by the adjacent carbonnanotubes. The apertures 105 can also be gaps formed by the adjacentcarbon nanotubes aligned parallel with each other along the axialdirection of the carbon nanotubes. If the apertures 105 are micro-holes,the diameter of the micro-hole range from about 10 nanometers to about500 micrometers. If the apertures 105 are gaps, the average width of thegap ranges from about 10 nanometers to about 500 nanometers. The carbonnanotube layer 102 can have both micro-holes and gaps at the same time.The diameter of the micro-hole and the width of the gap can bedifferent. In one embodiment, the apertures 105 uniformly distribute inthe carbon nanotube layer 102.

Both the diameter of the micro-hole and the width of the gap are definedas “the size of the apertures” in the following description. The size ofthe apertures 105 range from about 10 nanometers to about 500micrometers, such as 1 micrometer, 10 micrometer 80 micrometers, or 120micrometers. The smaller the size of the apertures 105, the fewerdislocations exist in the process of growing the epitaxial layer, andthe higher the quality of N-type semiconductor layer 106. In oneembodiment, the size of the apertures 105 range from about 10 nanometersto about 10 micrometers. Furthermore, the duty cycle of the carbonnanotube layer 102 ranges from about 1:100 to about 100:1 such as 1:10,1:2, 1:4, 4:1, 2:1, or 10:1. “Duty cycle” is defined as the area ratiobetween the epitaxial growth surface 101 which is covered by carbonnanotubes and the exposed surface which is exposed via the apertures105. In one embodiment, the duty cycle of the carbon nanotube layer 102ranges from about 1:4 to about 4:1.

The alignment of the carbon nanotubes in the carbon nanotube layer 102can be disorderly or orderly aligned to ensure that the carbon nanotubelayer 102 has the plurality of apertures 105. The disordered carbonnanotubes can be randomly aligned. The disordered carbon nanotubes canalso be entangled with each other. The ordered carbon nanotubes can bearranged approximately along a same direction or have two or moresections having carbon nanotubes within the section arrangedapproximately along a same direction (different sections can havedifferent directions). The plurality of carbon nanotubes can be alignedalong a crystal orientation of the substrate 100 or aligned at a certainangle with respect to the crystal orientation. In one embodiment, theplurality of carbon nanotubes in the carbon nanotube layer 102 isaligned parallel to the surface of the carbon nanotube layer 102. If thecarbon nanotube layer 102 is applied on the substrate 100, the pluralityof carbon nanotubes are aligned parallel to the epitaxial growth surface101.

The carbon nanotube layer 102 can directly grow on the epitaxial growthsurface 101 by a chemical vapor deposition (CVD) method. The carbonnanotube layer 102 can also be fabricated by growing the carbon nanotubearray on another substrate and transferred to the epitaxial growthsurface 101. In one embodiment, the carbon nanotube layer 102 is afree-standing structure, and the carbon nanotube layer 102 can beconveniently and directly placed on the substrate 100. The term“free-standing structure” means that the carbon nanotube layer 102 cansustain the weight of itself when it is hoisted by a portion thereofwithout any significant damage to its structural integrity. So, if thecarbon nanotube layer 102 is placed between two separate supports, aportion of the first carbon nanotube structure which does not in contactwith the two supports would be suspended between the two supports andmaintain structural integrity. The carbon nanotube layer 102 includes aplurality of carbon nanotubes distributed uniformly and attracted by vander Waals attractive force therebetween. The substrate 100 and thecarbon nanotube layer 102 can form a new substrate growing a N-typesemiconductor layer 106.

The carbon nanotube layer 102 can be a continuous and integratedstructure. The carbon nanotube layer 102 can also be a single layerstructure including a plurality of carbon nanotube wires. The pluralityof carbon nanotube wires can be parallel with each other. In thissituation, the plurality of carbon nanotube wires can form afree-standing structure by applying a support surface to each of thecarbon nanotube wires. Furthermore, the carbon nanotubes can be joinedend to end by van der Waals force along the aligned direction of thecarbon nanotubes, and adjacent carbon nanotubes parallel with each othercan also be joined by van der Waals force, thus the free-standingcharacter will be improved.

The carbon nanotube layer 102 can be a pure carbon nanotube structurecomposed only of a plurality of carbon nanotubes. The carbon nanotubelayer 102 is not functionalized or treated with acid. The carbonnanotube layer 102 can also be a composite structure composed of carbonnanotubes and additive material. The carbon nanotubes are used as themain component and provide some framework. The additive materialsinclude graphite, graphene, silicon carbide, boron nitride, siliconnitride, silicon dioxide, amorphous carbon, metal carbides, metaloxides, and metal nitrides. The additive materials can be partiallycoated on the surface the carbon nanotubes. In one embodiment, theadditive material is coated on the surface of the carbon nanotubes. Thusthe size of the apertures 105 is reduced. The additive materials can becoated on the carbon nanotubes by CVD, physical vapor deposition (PVD),or sputtering methods.

The carbon nanotube layer 102 can be preformed and then placed directlyplaced on the epitaxial growth surface 101. In one embodiment, thecarbon nanotube layer 102 can also be treated with an organic solventafter the carbon nanotube layer 102 is attached on the epitaxial growthsurface 101. The carbon nanotube layer 102 can be treated by drippingthe organic solvent onto the carbon nanotube layer 102 or putting thecarbon nanotube layer 102 into the organic solvent to soak the entiresurfaces of the carbon nanotube layer 102. During the surface treatment,the carbon nanotube layer 102 is attached firmly on the epitaxial growthsurface 101 due to factors such as surface tension. The organic solventscan be ethanol, methanol, acetone, dichloroethane, or chloroform. In oneembodiment, the organic solvent is ethanol.

The carbon nanotube layer 102 can include at least one carbon nanotubefilm or a plurality of carbon nanotube wires. If the carbon nanotubelayer 102 includes a plurality of carbon nanotube films, the carbonnanotube films are stacked together. In one embodiment, the carbonnanotube layer 102 includes about 2 layers to about 100 layers of carbonnanotube film. If the carbon nanotube layer 102 includes a plurality ofcarbon nanotube wires, the carbon nanotube wires can be aligned parallelto each other at a certain interval. The distance between adjacentcarbon nanotube wires ranges about 0.1 micrometer to about 200micrometers. In one embodiment, the distance ranges from about 10micrometers to about 100 micrometers. The gaps between the adjacentcarbon nanotube wires form the apertures 105 of the carbon nanotubelayer 102. In one embodiment, the carbon nanotube wires can also form across-network structure. Thus the size of the apertures 105 can becontrolled by the layers of carbon nanotube film or the distance betweenthe adjacent carbon nanotube wires.

In one embodiment, the carbon nanotube film can be a drawn carbonnanotube film which is a freestanding structure composed of a pluralityof carbon nanotubes. The carbon nanotubes are arranged substantiallyparallel to a surface of the drawn carbon nanotube film. A largemajority of the carbon nanotubes in the drawn carbon nanotube film canbe oriented along a preferred orientation, meaning that a majority ofthe carbon nanotubes in the carbon nanotube film are arrangedsubstantially along the same direction. An end of one carbon nanotube isjoined to another end of an adjacent carbon nanotube arrangedsubstantially along the same direction by the van der Waals force.

Some variations can occur in the orientation of the carbon nanotubes inthe drawn carbon nanotube film. Microscopically, the carbon nanotubesoriented substantially along the same direction may not be perfectlyaligned in a straight line, and some curved portions may exist. Contactbetween some carbon nanotubes placed substantially side by side andoriented along the same direction cannot be totally excluded.

Referring to FIG. 2 and FIG. 3, the drawn carbon nanotube film caninclude a plurality of successively oriented carbon nanotube segments143 joined end-to-end by the van der Waals force therebetween. Eachcarbon nanotube segment 143 includes a plurality of carbon nanotubes 145substantially parallel to each other, a joined by the van der Waalsforce therebetween, and oriented substantially along the same direction.The drawn carbon nanotube film can be drawn from a carbon nanotubearray. The carbon nanotube segments 143 can vary in width, thickness,uniformity, and shape. The carbon nanotubes 145 in the drawn carbonnanotube film are also substantially oriented along a preferredorientation. A thickness of the carbon nanotube film can range fromabout 1 nanometer to about 100 micrometers. In one embodiment, thethickness of the carbon nanotube film ranges from about 100 nanometersto about 10 micrometers. A width of the carbon nanotube film relates tothe carbon nanotube array from which the drawn carbon nanotube film isdrawn. In each carbon nanotube segment 143, a plurality of micro-holesor gaps exists between adjacent carbon nanotubes. These micro-holes orgaps form the apertures 105. The size of the apertures 105 is smallerthan 10 micrometers. Examples of a carbon nanotube film are taught byU.S. Pat. No. 7,045,108 to Jiang et al., and WO 2007015710 to Zhang etal.

Referring to FIG. 4, in one embodiment, the carbon nanotube layer 102includes at least two carbon nanotube films stacked with each other. Anangle between the aligned directions of the carbon nanotubes in the twoadjacent carbon nanotube films can range from about 0 degrees to about90 degrees (0°≦α≦90°).

The carbon nanotube film can be heated to reduce the thickness of thecarbon nanotube film. The carbon nanotube film can be heated part bypart to avoid destroying the carbon nanotube film. The heat treatmentcan include the following steps:

(S201) oxidizing some carbon nanotubes on a part of the carbon nanotubefilm by providing a heating device and heating the part of the carbonnanotube film with the heating device; and

(S202) heating the carbon nanotube film part by part by moving thedevice.

Specifically, the carbon nanotube film can be divided into several partsand heated part by part. The carbon nanotube can be heated by a laser ormicrowaves. In one embodiment, the carbon nanotube film is irradiated bya laser device. Irradiated larger diameter carbon nanotubes will beremoved, thereby reducing the thickness of the carbon nanotube film.

It is to be understood that the ways of laser irradiating are arbitrary.The movement of the laser device can be substantially parallel orperpendicular to the aligned direction of the carbon nanotubes. Using alaser device with a stable power density, the slower the moving speed ofthe laser device, the more carbon nanotubes of the carbon nanotube filmwill be destroyed, and the thinner the carbon nanotube film. However, ifthe speed is too slow, the carbon nanotube film will be completelydestroyed. In one embodiment, a power density of the laser is greaterthan 0.053×10¹² W/m², a diameter of the irradiating pattern of the laserranges from about 1 micrometer to about 5 millimeters, and a time oflaser irradiation is less than 1.8 s. In one embodiment, the laser is acarbon dioxide laser, the power of the laser is about 30 W, a wavelengthof the laser is about 10.6 microns, the diameter of the irradiatingpattern of the laser is about 3 millimeters, and a moving speed of thelaser device is less than 10 m/s.

The carbon nanotube wire includes untwisted carbon nanotube wire andtwisted carbon nanotube wire. Referring to FIG. 5, the untwisted carbonnanotube wire includes a number of carbon nanotubes substantiallyparallel to each other. The untwisted carbon nanotube wire can be formedby treating the drawn carbon nanotube film with an organic solvent. Thedrawn carbon nanotube film is treated by applying the organic solvent tothe carbon nanotube film to soak the surface of the drawn carbonnanotube film without adhering on the substrate. After being soaked bythe organic solvent, the adjacent paralleled carbon nanotubes in thedrawn carbon nanotube film will bundle together, due to the surfacetension of the organic solvent as the organic solvent volatilizes, andthus, the drawn carbon nanotube film will shrink into untwisted carbonnanotube wire. Examples of the untwisted carbon nanotube wire are taughtby U.S. Pat. No. 7,045,108 to Fan et al. and US publication No.20070166223 A1 to Fan et al.

Referring to FIG. 6, the twisted carbon nanotube wire can be formed bytwisting a drawn carbon nanotube film by using a mechanical force toturn the two ends of the drawn carbon nanotube film in oppositedirections. The twisted carbon nanotube wire can be treated by applyingthe organic solvent thereon to bundle together adjacent paralleledcarbon nanotubes in the twisted carbon nanotube film. The treatedtwisted carbon nanotube wire may have less specific surface area, andgreater density and strength than a non-treated twisted carbon nanotubewire.

As discussed above, the carbon nanotube layer 102 can be used as a maskfor growing the semiconductor epitaxial layer 104. The term ‘mask forgrowing the semiconductor epitaxial layer 104’ means that the carbonnanotube layer 102 can be used to shelter a part of the epitaxial growthsurface 101 and expose the other part of the epitaxial growth surface101. Thus, the semiconductor epitaxial layer 104 can grow from theexposed epitaxial growth surface 101. The carbon nanotube layer 102 canform a patterned mask on the epitaxial growth surface 101 because thecarbon nanotube layer 102 defines a plurality of first apertures 105.Compared to lithography or etching, the method of forming a carbonnanotube layer 102 with masking is simple, low in cost, and will notpollute the substrate 100. If the carbon nanotube layer 102 is placed onthe epitaxial growth surface 101, the carbon nanotubes of the carbonnanotube layer 102 will be substantially parallel to the epitaxialgrowth surface 101.

A buffer layer and an intrinsic layer (not shown) can be deposited onthe epitaxial growth surface 101 before the step (S20). The quality ofthe semiconductor epitaxial layer 104 can be improved through this step.

In step (S30), the semiconductor epitaxial layer 104 grows via a processof molecular beam epitaxy (MBE), chemical beam epitaxy (CBE), vacuumepitaxy, low temperature epitaxy, choose epitaxy, liquid phasedeposition epitaxy (LPE), metal organic vapor phase epitaxy (MOVPE),ultra-high vacuum chemical vapor deposition (UHVCVD), hydride vaporphase epitaxy (HYPE), and metal organic chemical vapor deposition(MOCVD). The semiconductor epitaxial layer 104 is a layer of singlecrystal structure growing on the epitaxial growth surface 101. Thematerial of the semiconductor epitaxial layer 104 can be the same as thesubstrate 100. If the material is the same, the semiconductor epitaxiallayer 104 is the homoepitaxial layer, otherwise the semiconductorepitaxial layer 104 is the heteroepitaxial layer. The thickness of thesemiconductor epitaxial layer 104 can be selected according to need. Inone embodiment, the semiconductor epitaxial layer 104 has a thicknessranging from about 100 nanometers to about 500 micrometers, such asabout, 500 nanometers, 1 micrometer, 2 micrometers, 5 micrometers, 10micrometers, and 50 micrometers. The material of the semiconductorepitaxial layer 104 can be Si, GaAs, GaN, GaSb, InN, InP, InAs, InSb,AlP, AlAs, AlSb, AlN, GaP, SiC, SiGe, GaMnAs, GaAlAs, GaInAs, GaAlN,GaInN, AlInN, GaAsP, InGaN, AlGaInN, AlGaInP, GaP:Zn, or GaP:N.

The N-type semiconductor layer 106 and the P-type semiconductor layer108 are a doped semiconductor epitaxial layer. The active layer 107 is aphoton excitation layer and can be one of a single layer quantum wellfilm or multilayer quantum well films. The N-type semiconductor layer106, the active layer 107, and the P-type semiconductor layer 108 arestacked on the epitaxial growth surface 101, and the active layer 107 issandwiched between the N-type semiconductor layer 106 and the P-typesemiconductor layer 108. The P-type semiconductor layer 108 can firstlygrow on the substrate 100, and the active layer 107, the N-typesemiconductor layer 106 can grow on the P-type semiconductor layer 108.In one embodiment, the material of the N-type semiconductor layer 106,the active layer 107, and the P-type semiconductor layer 108 is thesame, thus defects caused by dislocation during the growth process willbe reduced.

In one embodiment, the semiconductor epitaxial layer 104 is doped viaintroducing different doped gas into the source gas. The N-typesemiconductor layer 106, the active layer 107 and the P-typesemiconductor layer 108 can grow in series by changing the doped gas andcontrolling the grow time. Referring to FIG. 7, the growth of thesemiconductor epitaxial layer 104 can include the following steps:

(S31) growing a plurality of epitaxial crystal nucleus on the epitaxialgrowth surface 101, and forming from the epitaxial crystal nucleus aplurality of epitaxial crystal grains 1042 along the directionsubstantially perpendicular to the epitaxial growth surface 101;

(S32) growing from the plurality of epitaxial crystal grains 1042 acontinuous epitaxial film 1044 along the direction substantiallyparallel to the epitaxial growth surface 101;

(S33) forming the N-type semiconductor layer 106, the active layer 107,and the P-type semiconductor layer 108 by growing continuously theepitaxial film 1044 along the direction substantially perpendicular tothe epitaxial growth surface 101; and

(S34) annealing the semiconductor epitaxial layer 104.

In step (S31), because the carbon nanotube layer 102 is placed on theepitaxial growth surface 101, the epitaxial crystal grains 1042 can onlygrow on the epitaxial growth surface 101 which are exposed out of thecarbon nanotube layer 102 through the apertures 105. The growthdirection of the epitaxial crystal grains 1042 is substantiallyperpendicular to the surface of the epitaxial growth surface 101.

In step (S32), the epitaxial crystal grains 1042 can grow out of theapertures 105 of the carbon nanotube layer 102 along the directionsubstantially parallel to the epitaxial growth surface 101. Thus theepitaxial crystal grains 1042 will form an integrated structure such asthe epitaxial film 1044. During this process, a plurality of grooves 103will be formed in the epitaxial film 1044. The carbon nanotubes areembedded in the grooves 103. If the carbon nanotube layer 102 is asingle layer of carbon nanotube film or a plurality of carbon nanotubewires substantially parallel with each other, the grooves 103 are alsosubstantially parallel with each other. If the carbon nanotube layer 102includes a plurality of carbon nanotube films are stacked in a crossedorder or a plurality of carbon nanotube wires intersect each other, thegrooves 103 intersect each other to form a network structure. In oneembodiment, the grooves 103 form a patterned N-type semiconductor layer106 similar to that of the carbon nanotube layer 102. The distancebetween the two adjacent grooves 103 ranges from about 0.5 nanometers toabout 100 micrometers, such as about, 1 nanometer, 10 nanometers, 50nanometers, 1 micrometer, 10 nanometers, or 50 nanometers.

The carbon nanotubes of the carbon nanotube layer 102 can partly contactthe N-type semiconductor layer 106 to electrically connect with theN-type semiconductor layer 106. The material of the N-type semiconductorlayer can have good wettability with the carbon nanotubes, thus thecarbon nanotube layer 102 will firmly contact the N-type semiconductorlayer 106. Furthermore, the carbon nanotubes are coated with a layer ofconductive material such as a doped SiC. Because the doped SiC has agood conductivity, the conductivity between the carbon nanotube layer102 and the N-type semiconductor layer will be improved.

In step (S33), the dislocation between the epitaxial crystal grains 1042and the substrate 100 will be reduced, and the quality of the epitaxialfilm 1044 will be improved, because of the carbon nanotube layer 102.The N-type semiconductor layer 106 homoepitaxially grows on theepitaxial film 1044, thus the N-type semiconductor layer 106 includesless defects. Furthermore, the quality of the active layer 107 and theP-type semiconductor layer 108 will also be improved.

The semiconductor epitaxial layer 104 can be doped by introducing thedoped source gas. The material, doped element, and the doped ratio ofthe semiconductor epitaxial layer 104 can be selected by controlling thesource gas. The thickness of the N-type semiconductor layer 106, theactive layer 107, and the P-type semiconductor layer 108 can be selectedseparately by controlling the growth time. In one embodiment, thematerial of the semiconductor epitaxial layer 104 is GaN.

Furthermore, the method further includes a step of growing a layer ofhighly doped contact electrode (not shown). The highly doped contactelectrode can be obtained by raising the doping ratio of the dopedelements in the source gas. The N-type semiconductor layer 106, theactive layer 107, the P-type semiconductor layer 108 and the contactelectrode form the semiconductor epitaxial layer 104 together.

In step (S34), the doped elements in the semiconductor epitaxial layer104 is activated in the annealing process. The annealing process isprocessed in a temperature range from about 700° C. to about 1100° C.under protective atmosphere for about 10 minutes to about 20 minutes.

In step (S40), the semiconductor epitaxial layer 104 can be etched bythe following steps:

(S41) coating a layer of photo resist uniformly on the semiconductorepitaxial layer 104;

(S42) prebaking the photo resist in a temperature ranging from about 80°C. to about 100° C. for about 20 minutes to about 30 minutes;

(S43) exposing and developing the photo resist;

(S44) baking the photo resist in a temperature ranging from about 100°C. to about 150° C. for about 20 minutes to about 30 minutes;

(S45) corroding the semiconductor epitaxial layer 104 to form apredetermined figure; and

(S46) removing the photo resist by immersing the photo resist into asolvent.

The step (S43) can further include the following substeps:

(S431) placing a mask layer on the surface of the semiconductorepitaxial layer 104;

(S442) irradiating the semiconductor epitaxial layer 104 usingultraviolet;

(S443) immersing the semiconductor epitaxial layer 104 into a developerfor about 30 minutes to obtain a patterned photo resist.

A plurality of LEDs can be obtained by etching the semiconductorepitaxial layer 104 via the patterned photo resist.

In step (S50), the first electrode 110 and the second electrode 112 canbe an N-type electrode or a P-type electrode. The thickness of the firstelectrode 110 and the second electrode 112 ranges from about 0.01micrometers to about 2 micrometers. The first electrode 110 and thesecond electrode 112 can also function as a reflector. The material ofthe first electrode 110 and the second electrode 112 can be titanium(Ti), silver (Ag), aluminum (Al), nickel (Ni), gold (Au), or anycombination of them. The material of the first electrode 110 and thesecond electrode 112 can also be indium-tin oxide (ITO) or carbonnanotube film. The first electrode 110 can cover the entire surface or apart of the surface of the P-type semiconductor layer 108. The firstelectrode 110 and the second electrode 112 can be made by an etchingprocess with a mask layer.

Because the material of the first electrode 110 and the second electrode112 is a metal or alloy, the material can be selected separatelyaccording to the semiconductor layer electrically connected with thefirst electrode 110. Thus the contact resistance will be reduced. Thefirst electrode 110 and the second electrode 112 can be deposited via aprocess of physical vapor deposition, such as electron beam evaporation,vacuum evaporation, ion sputtering, or any physical deposition. Whilethe light is extracted from the P-type semiconductor layer 108, thefirst electrode 110 should only cover a part of the surface of theP-type semiconductor layer 108. The ratio of the surface of the P-typesemiconductor layer 108 which is covered by the first electrode rangesfrom about 10% to about 15%.

The second electrode 112 covers the entire surface of the carbonnanotube film 102. While the light is extracted from the substrate 100,the first electrode can cover the entire surface of the P-typesemiconductor layer 108, and the second electrode 112 can cover theentire surface of the carbon nanotube film 102.

If the material of the first electrode 110 and the second electrode 112is ITO, the first electrode 110 and the second electrode 112 can bedeposited via magnetron sputtering, evaporation, spraying, or sol-gelmethod. The first electrode 110 can cover the entire surface of theP-type semiconductor layer 108, and the second electrode 112 can alsocover the entire surface of the carbon nanotube layer 102.

The carbon nanotube layer 102 and the second electrode 112 should have agood electrical connection. Whether the carbon nanotube layer 102includes a plurality of carbon nanotube layers stacked and intersectingeach other, or a plurality of carbon nanotube wires intersecting eachother, the carbon nanotubes in the entire carbon nanotube layer 102 areelectrically connected with each other to form an integrated conductor.In one embodiment, the second electrode 112 is connected with an edge ofthe carbon nanotube layer 102 or four corners of the carbon nanotubelayer 102. If the carbon nanotube layer 102 includes a single layer ofcarbon nanotube film or a plurality of carbon nanotube wiressubstantially parallel with each other, the carbon nanotubes in thecarbon nanotube layer 102 are substantially oriented in the samedirection. Because the conductivity between the two adjacent carbonnanotube wires parallel to each other is small, the second electrode 112should be electrically connected to each of the carbon nanotube wires.In one embodiment, the extending direction of the second electrode 112is substantially perpendicular to the extending direction of the carbonnanotubes.

Furthermore, a surface of the semiconductor epitaxial layer 104 can beroughened before step (S50). The surface of the semiconductor epitaxiallayer 104 could be roughened by an etching process or irradiation with alaser to reduce the total reflection during the light extraction. Themethod of roughening the surface of the semiconductor epitaxial layer104 can be processed according to the step (S31). A carbon nanotubelayer is first placed on the semiconductor epitaxial layer 104. A layerof epitaxial crystal grains is then grown. The epitaxial crystal grainsare discontinuous. The layer of epitaxial crystal grains defines as apatterned microstructure similar to that of the carbon nanotube layer102. The microstructures can be a plurality of grooves substantiallyparallel or intersecting each other. The distance between two adjacentgrooves ranges from about 0.5 nanometers to about 100 micrometers, suchas about, 1 nanometer, 10 nanometers, 50 nanometers, 100 nanometers, 1micrometer, 10 micrometer, or 50 nanometers. The carbon nanotube layer102 can be used as the first electrode 110 or removed by heated inoxygen.

Different examples will be described in the following paragraphs.

EXAMPLE 1

Referring to FIG. 8 and FIG. 9, a LED 10 includes a substrate 100, acarbon nanotube layer 102, a semiconductor epitaxial layer 104, a firstelectrode 110, and a second electrode 112. The semiconductor epitaxiallayer 104 includes an N-type semiconductor layer 106, an active layer107, and a P-type semiconductor layer 108.

The substrate 100 includes an epitaxial growth surface 101. The carbonnanotube layer 102 is placed on the epitaxial growth surface 101. TheN-type semiconductor layer 106, the active layer 107 and the P-typesemiconductor layer 108 are stacked on the same side of the epitaxialgrowth surface 101 in that order and cover a part of the carbon nanotubelayer 102. The carbon nanotube layer 102 are partly sandwiched betweenthe N-type semiconductor layer 106 and the substrate 100, and partlyexposed from the semiconductor epitaxial layer 104. The second electrode112 is electrically connected with the exposed part of the carbonnanotube layer 102. The location of the N-type semiconductor layer 106and the P-type semiconductor layer 108 can be exchanged.

The carbon nanotube layer 102 is a continuous and integrated structure.The N-type semiconductor layer 106 is electrically connected with thecarbon nanotube layer 102. The carbon nanotube layer 102 defines aplurality of apertures 105. The substrate 100 is partly exposed to thesemiconductor epitaxial layer 104 from the apertures 105. The N-typesemiconductor layer 106 penetrates the carbon nanotube layer 105 throughthe apertures 105 and connects with the substrate 100. Thus the N-typesemiconductor layer 106 is placed on the substrate 100 through theapertures 105. The surface of the N-type semiconductor layer 106, whichis connected with the substrate 100 includes a plurality of grooves 103.The plurality of grooves 103 are blind holes along the extendingdirection of the thickness of the semiconductor epitaxial layer 104. Thecarbon nanotubes of the carbon nanotube layer 102 are embedded in thegrooves 103. The grooves 103 can be substantially parallel with eachother or intersect each other to form a network structure. If the lightexcited from the active layer 107 reaches the interface between theN-type semiconductor layer 106 and the substrate 100 at a sufficientlylarge incident angle, the light will be scattered. The extractingdirection of the light will be changed by the grooves 103 and the carbonnanotubes, thus the light can be extracted from the LED 10, and thelight extraction efficiency will be improved.

The N-type semiconductor layer 106 is configured to provide electrons,and the P-type semiconductor layer 108 is configured to provide holes.The active layer 107 is configured to provide photons. The firstelectrode 110 and the second electrode 112 are configured to apply avoltage. The first electrode 110 is used as the upper electrode of theLED 10, and the second electrode 110 is used as the lower electrode. Thecarbon nanotube layer 102 is electrically connected to the entiresurface of the N-type semiconductor layer 106. The first electrode 110can cover the entire surface of the P-type semiconductor layer 108, andthe second electrode 112 is electrically connected to the carbonnanotube layer 102. When applying a voltage between the first electrode110 and the second electrode 112, the current flows from the upperelectrode to the lower electrode. Thus the LED 10 forms in a verticalstructure. The light can be extracted from the P-type semiconductorlayer 108. If the first electrode 110 covers a part of the surface ofthe P-type semiconductor layer 108, the LED 10 forms in a horizontalstructure. Because the carbon nanotube layer 102 covers the entiresurface of the N-type semiconductor layer 106, the current flowing routein the LED 10 is shorter than the conventional LED, the energyconsumption is reduced and the power can be improved.

In one embodiment, the material of the substrate 100 is sapphire(Al₂O₃). The carbon nanotube layer 102 includes two layers of carbonnanotube film stacked and intersecting each other. Each carbon nanotubefilm includes a plurality of carbon nanotubes oriented along a preferredorientation. An end of one carbon nanotube is joined to another end ofan adjacent carbon nanotube arranged substantially along the samedirection by the van der Waals force. In one embodiment, the preferredorientation of the carbon nanotubes in one carbon nanotube layer issubstantially perpendicular to another carbon nanotube layer thereof.The apertures 105 are formed between the adjacent carbon nanotubes inthe direction substantially perpendicular to the preferred orientation.The N-type semiconductor layer 106 is GaN doped with Si, and thethickness ranges from about 1 micrometer to about 5 micrometers. Theactive layer 107 is multilayer quantum well films which include onelayer of GaInN and another layer of GaN. The thickness of the activelayer 107 ranges from about 0.01 micrometers to about 0.6 micrometers.The P-type semiconductor layer 108 is GaN doped with Mg, and thethickness ranges from about 0.1 micrometers to about 3 micrometers. Thefirst electrode 110 is an ITO transparent electrode in a thickness ofabout 50 nanometers. The first electrode 110 covers the entire surfaceof the P-type semiconductor layer 108. The second electrode 112 is anN-type electrode placed on the exposed surface of the carbon nanotubelayer 102. The second electrode 112 includes one layer of Ti in athickness of about 150 angstroms and another layer of Au in a thicknessof about 2000 angstroms.

In one embodiment, the semiconductor epitaxial layer 104 is made by theMOCVD method. In the MOCVD method, the nitrogen source gas ishigh-purity ammonia (NH₃), the carrier gas is hydrogen (H₂), the Gasource gas is trimethyl gallium (TMGa) or triethyl gallium (TEGa), andthe Si source gas is silane (SiH₄). The growth of the semiconductorepitaxial layer 104 can include the following steps:

(a) placing the substrate 100 into a furnace and heating the substrate100 to about 1100° C. to about 1200° C., introducing the carrier gas,and baking the substrate 100 for about 200 seconds to about 1000seconds;

(b) introducing the Ga source gas and the nitrogen source gas at thesame time and cooling down the temperature to a range from about 500° C.to 650° C. and keeping the pressure range from 500 torr to about 600torr in the carrier gas atmosphere to grow a low-temperature GaN bufferlayer, and the thickness of the buffer layer ranges from about 10nanometers to about 50 nanometers;

(c) stopping the flow of the Ga source gas in the carrier gas andnitrogen source gas atmosphere, increasing the temperature to a rangefrom about 1100° C. to about 1200° C., and maintaining for about 30seconds to about 300 seconds to anneal the substrate 100;

(d) maintaining the temperature at a range from about 1000° C. to about1100° C. and the pressure range from about 100 torr to about 300 torr,and reintroducing the Ga source gas and introducing the Si source gas togrow the high quality GaN layer doped with Si;

(e) stopping the flow of the Si source gas and maintaining thetemperature of the reaction furnace to a range from about 700° C. toabout 900° C., and the pressure of the reaction furnace to a range fromabout 50 torrs to about 500 torrs, and introducing the indium source gassimultaneously to grow InGaN/GaN multilayer quantum well film, whereinthe thickness of the InGaN ranges from about 2 nanometers to about 5nanometers, and the thickness of the GaN ranges from about 5 nanometersto about 20 nanometers;

(f) stopping the flow of the indium source gas and maintaining thetemperature of the reaction furnace at a range from about 1000° C. toabout 1100° C., and the pressure of the reaction furnace at a range fromabout 76 torrs to about 200 torrs; and introducing the Mg source gas atthe same time to grow P-type GaN layer doped with Mg;

(g) stopping the flow of the source gas and annealing the substrate 100in a temperature ranging from about 700° C. to about 800° C. in N₂atmosphere for about 10 minutes to about 20 minutes;

(h) etching the GaN epitaxial layer to expose part of the surface of thecarbon nanotube layer 102;

(i) depositing an ITO layer having a thickness of about 50 nanometers onthe surface of the P-type GaN layer;

(j) depositing a Ni layer and an Au layer on the exposed part of thecarbon nanotube layer 102, in which the thickness of the Ni layer isabout 150 angstroms and the Au is about 2000 angstroms.

Furthermore, a layer of P-type AlGaN doped with Mg can be grown beforestep (f). The temperature of the furnace is maintained at about 1000° C.to about 1100° C., and the pressure of the furnace is maintained atabout 76 torr to about 200 torr. The trimethyl Aluminum is introducedinto the furnace to grow the AlGaN with a thickness ranging from about30 nanometers to about 50 nanometers.

After the step (g), the sample is scanned by the SEM and the TEM.Referring to FIG. 10 and FIG. 11, the N-type semiconductor layer canonly grow on the substrate not covered by the carbon nanotubes. Aplurality of holes is formed between the N-type semiconductor layer andthe substrate. FIG. 10 shows the cross-section of the junction betweenthe N-type semiconductor layer and the sapphire substrate. The darkportion is the N-type semiconductor layer, and the lighter portion isthe sapphire substrate. Referring to FIG. 11, the carbon nanotubes existin each hole, and the carbon nanotubes are attached on the substrate andcontacted with the N-type semiconductor layer.

Embodiment 2

Referring to FIG. 12, a LED 20 includes a substrate 100, a carbonnanotube layer 102, a semiconductor epitaxial layer 104, a firstelectrode 110, and a second electrode 112. The semiconductor epitaxiallayer 104 includes an N-type semiconductor layer 106, an active layer107, and a P-type semiconductor layer 108. The LED 20 is similar to theLED 10 except that the first electrode 110 is configured as thereflector. The first electrode 110 covers the entire surface of theP-type semiconductor layer 108. While the LED is working, the light isextracted from the sapphire substrate.

The first electrode 110 includes a super smooth and plane surface toimprove the reflection efficiency. In one embodiment, the firstelectrode 110 is a metallic reflector film. The material of the firstelectrode 110 can be selected from Ti, Ag, Al, Ni, Au or any alloy ofthem such as Au/AuBe or Au/Cu/Al. The thickness of the first electrode110 can be selected according to need. In one embodiment, the firstelectrode 110 ranges from about 50 nanometers to about 250 nanometers inthickness, wherein the Ni ranges from about 10 nanometers to about 50nanometers in thickness, the Cu ranges from about 20 nanometers to about50 nanometers in thickness and the Al ranges from about 30 nanometers toabout 150 nanometers. In another embodiment, the first electrode 110 isa multilayer structure composed of Ni/Cu/Al. The Al layer is attached onthe surface of P-type semiconductor layer 108. The thickness of thefirst electrode is about 140 nanometers wherein the Ni is about 20nanometers, the Cu is about 20 nanometers and the Al is about 100nanometers in thickness. When the photons from the active layer 107reach the first electrode 110, the photons will be reflected. The firstelectrode 10 can also be a metallic plate with high conductivity. Themetallic plate can function as the reflector, the heat sink, and theelectrode.

The LED is sealed into a flip chip structure, and the surface of thesapphire is used as the light extraction surface. Because the firstelectrode 110 reflects all the photons incidental to the P-typesemiconductor layer 108, the light will be extracted from the sapphire,and the light extraction efficiency of the LED will be improved.

It is understood that, if the light excited from the active layer 107reaches the interface between the N-type semiconductor layer 106 and thesubstrate 100 at a sufficiently large incident angle, the light will bescattered. The extracting direction of the light will be changed by thegrooves 103 and the carbon nanotubes, thus the light can be extractedfrom the LED 10, and the light extraction efficiency will be improved.Furthermore, a heat sink can be applied on the first electrode toextract the heat.

The method for making the LED 20 is similar to the method for making theLED 10.

Embodiment 3

Referring to FIG. 13, an LED 30 includes a substrate 100, a carbonnanotube layer 102, a semiconductor epitaxial layer 104, a firstelectrode 110, and a second electrode 112. The semiconductor epitaxiallayer 104 includes an N-type semiconductor layer 106, an active layer107, and a P-type semiconductor layer 108. The LED 30 is similar to theLED 10 except that an intrinsic semiconductor layer 114 is sandwichedbetween the N-type semiconductor layer 106 and the substrate 100. Thecarbon nanotube layer 102 is sandwiched between the N-type semiconductorlayer 106 and the intrinsic semiconductor layer 114.

The method for making the LED 30 is similar to the LED 10 except that abuffer layer (not shown) and the intrinsic semiconductor layer 114 aregrown on the epitaxial growth surface 101. The carbon nanotube layer 102is placed on the intrinsic semiconductor layer 114, and the N-typesemiconductor layer 106, the active layer 107, and the P-typesemiconductor layer 108 are grown on the intrinsic semiconductor layer114 in that order.

Embodiment 4

Referring to FIG. 14, an LED 40 in one embodiment includes a substrate100, a carbon nanotube layer 102, a semiconductor epitaxial layer 104, afirst electrode 110, and a second electrode 112. The semiconductorepitaxial layer 104 includes an N-type semiconductor layer 106, anactive layer 107 and a P-type semiconductor layer 108. The LED 40 issimilar to the LED 10 except that the carbon nanotube layer 110 includesa plurality of carbon nanotube wires. The plurality of carbon nanotubewires is substantially parallel and spaced with each other. Theapertures 105 are formed between the two adjacent carbon nanotube wires.

The carbon nanotube wires can be untwisted carbon nanotube wires ortwisted carbon nanotube wires. The untwisted carbon nanotube wiresinclude a plurality of carbon nanotubes extending along the extenddirection of the carbon nanotube wires. The twisted carbon nanotubewires include a plurality of carbon nanotubes spinning and extendingaround the axis of the carbon nanotube wires.

In the method for making the LED 40, the semiconductor epitaxial layer104 is etched along the direction substantially perpendicular to theextending direction of the carbon nanotube wires. A portion of eachcarbon nanotube wires is exposed. The exposed portion of the carbonnanotube wire is electrically connected to the second electrode 112,thus the carbon nanotube layer 102 forms an integrated conductivestructure. The second electrode 112 forms a strip-like structure. Theextending direction of the second electrode 112 is substantiallyperpendicular to the extending direction of the carbon nanotube wires.

Embodiment 5

Referring to FIG. 15, an LED 50 in one embodiment includes a substrate100, a carbon nanotube layer 102, a semiconductor epitaxial layer 104, afirst electrode 110, and a second electrode 112. The semiconductorepitaxial layer 104 includes an N-type semiconductor layer 106, anactive layer 107 and a P-type semiconductor layer 108. The LED 50 issimilar to the LED 10 except that the carbon nanotube layer 110 includesa plurality of carbon nanotube wires. The plurality of carbon nanotubewires is spaced and intersecting each other. Each aperture is defined byfour adjacent and intersecting carbon nanotube wires.

Some carbon nanotube wires extend along a first direction and somecarbon nanotube wires extend along a second direction. The firstdirection and the second direction intersect each other. A portion ofthe carbon nanotube wires extending along the first direction isexposed, and the exposed portion of the carbon nanotube wires iselectrically connected to the second electrode 112. In one embodiment,the first direction is substantially perpendicular to the seconddirection. The first direction and the second direction intersect atarbitrary angles, to ensure the carbon nanotube layer 102 includes aplurality of apertures 105 to expose a portion of the substrate 100.

The method for making the LED has many advantages. One, the carbonnanotube layer is a continuous and free-standing structure, and it canbe directly placed on the substrate to grow an epitaxial layer. Theprocess is simple and the complex sputtering process is avoided. Aplurality of microstructures can also be formed on the light extractionsurface of the LED using carbon nanotube layers as the mask layer,thereby avoiding any complex etching process. Another is the aperturesin the carbon nanotube layer and the microstructures are sufficientlysmall such that the light extraction efficiency is improved. Yet anotheris because the etching process is avoided, damage to the latticestructure of the LED will be reduced.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. The description and the claims drawn to a method may includesome indication in reference to certain steps. However, the indicationused is only to be viewed for identification purposes and not as asuggestion as to an order for the steps.

The above-described embodiments are intended to illustrate rather thanlimit the disclosure. Variations may be made to the embodiments withoutdeparting from the spirit of the disclosure as claimed. Any element ofany one embodiment is considered to be disclosed to be incorporated withany other embodiment. The above-described embodiments illustrate thescope of the disclosure but do not restrict the scope of the disclosure.

1. A light emitting diode, comprising: a substrate comprising anepitaxial growth surface; a carbon nanotube layer located on theepitaxial growth surface; a semiconductor epitaxial layer comprising asecond semiconductor layer, an active layer, and a first semiconductorlayer stacked on the substrate in sequence, wherein a first part of thecarbon nanotube layer is covered by the first semiconductor layer and asecond part of the carbon nanotube layer is exposed; a first electrodeelectrically connected with the second semiconductor layer; and a secondelectrode electrically connected with the second part of the carbonnanotube layer.
 2. The light emitting diode of claim 1, wherein thecarbon nanotube layer is a continuous and integrated structure.
 3. Thelight emitting diode of claim 2, wherein the carbon nanotube layercomprises a plurality of carbon nanotubes extending substantiallyparallel with a surface of the carbon nanotube layer and the epitaxialgrowth surface.
 4. The light emitting diode of claim 3, wherein thecarbon nanotube layer comprises a carbon nanotube film, the carbonnanotube film comprises a plurality of carbon nanotubes orientedsubstantially along the same direction and joined end to end by van derWaals force.
 5. The light emitting diode of claim 4, wherein the carbonnanotube layer comprises a plurality of carbon nanotube films stackedtogether.
 6. The light emitting diode of claim 1, wherein the carbonnanotube layer comprises a plurality of carbon nanotube wiressubstantially parallel with each other.
 7. The light emitting diode ofclaim 1, wherein the carbon nanotube layer comprises a plurality ofcarbon nanotube wires, some of the carbon nanotube wires extend along afirst direction and the rest of the carbon nanotube wires extend along asecond direction, the first direction and the second directionintersecting each other.
 8. The light emitting diode of claim 1, whereinthe carbon nanotube layer defines a plurality of apertures, and thefirst semiconductor layer contacts the epitaxial growth surface throughthe apertures.
 9. The light emitting diode of claim 8, wherein a size ofthe apertures ranges from about 20 nanometers to about 500 nanometers.10. The light emitting diode of claim 8, wherein a plurality of groovesis defined on a surface of the first semiconductor layer contacting thesubstrate, and the carbon nanotube layer is embedded in the grooves. 11.The light emitting diode of claim 10, wherein the grooves aresubstantially parallel with each other or intersecting each other. 12.The light emitting diode of claim 10, wherein the carbon nanotube layeris electrically connected with the first semiconductor layer.
 13. Thelight emitting diode of claim 1, wherein the first electrode covers theentire surface of the second semiconductor layer, and the secondelectrode covers the entire surface of the second part of the carbonnanotube layer.
 14. The light emitting diode of claim 1, wherein thesecond semiconductor layer defines a plurality of grooves substantiallyparallel or intersecting each other on a surface far away from thesubstrate.
 15. The light emitting diode of claim 1, further comprisingan intrinsic semiconductor layer sandwiched between the firstsemiconductor layer and the substrate, and the carbon nanotube layer issandwiched between the first semiconductor layer and the intrinsicsemiconductor layer.
 16. The light emitting diode of claim 1, whereinthe carbon nanotube layer comprises a plurality of carbon nanotubes anda doped silicon carbide conductive layer coated on the carbon nanotubes.17. A light emitting diode, comprising: a substrate comprising anepitaxial growth surface; a semiconductor epitaxial layer comprising asecond semiconductor layer, an active layer, and a first semiconductorlayer stacked on the substrate in sequence, wherein a first part of theepitaxial growth surface is covered by the first semiconductor layer,and a second part of the epitaxial growth surface is exposed; a firstelectrode electrically connected with the second semiconductor layer; asecond electrode electrically connected with first semiconductor layer;and a patterned carbon nanotube layer sandwiched between the firstsemiconductor layer and the substrate, wherein the carbon nanotube layeris a continuous and integrated structure and extends to cover the secondpart of the epitaxial growth surface, and the second electrode coversthe carbon nanotubes layer corresponding to the second part of theepitaxial growth surface.
 18. The light emitting diode of claim 17,wherein the carbon nanotube layer defines a plurality of apertures andthe first semiconductor layer is contacting the epitaxial growth surfacethrough the apertures.
 19. The light emitting diode of claim 17, whereinthe first semiconductor layer is a patterned semiconductor layer whichdefines a plurality of grooves on a surface connected to the epitaxialgrowth surface, and the pattern of the patterned first semiconductorlayer is with the same as the pattern of the carbon nanotube layer. 20.The light emitting diode of claim 19, wherein the pattern firstsemiconductor layer defines a plurality of grooves substantiallyparallel with each other or intersecting each other.